To make the onion marmalade, in a 10-inch (25-cm) frying pan over medium heat, warm the olive oil. Add the onions, maple syrup, rosemary, vinegar, and pepper flakes and stir to coat the onions well. Season with salt and pepper. Reduce the heat to low and simmer, stirring occasionally, until the onions are soft and have absorbed all the liquid, about 30 minutes.

Meanwhile, warm a grill pan over medium-high heat. Lay the steaks on a plate, drizzle both sides with the oil, and season with salt and pepper.

When the pan just begins to smoke, add the steaks and cook until the meat is well browned, about 4 minutes. Turn the steaks and cook for 4 minutes longer for medium rare or until cooked to your liking.

Turn off the heat and loosely cover the pan with foil. Let the meat rest for 10 minutes to redistribute the juices.

Slice the steaks and serve right away with the onion marmalade.

Thick onion marmalade, spiked with red pepper flakes to offset its sweetness, makes a tempting sweet-spicy partner for juicy pan-grilled steaks. Any remaining marmalade can be spread on sandwiches or served with other pan-grilled meats.